CTENOPHORES OF THE ATLANTIC COAST OF NORTH AMERICA 7 



they constitute a serious menace to the cod fisheries by devouring the 

 pelagic eggs and young fish. 



The elucidation of the minute anatomy of ctenophores has been one 

 of the greatest triumphs of modem histology, and one with which one 

 associates the names of Fol, Chun, R. Hertwig, Samassa, Grabe, and 

 Bethe. 



Samassa was unable to demonstrate the existence of a nervous sys- 

 tem in Ctenophores, but Bethe, 1895 (Biol. Centralblatt, Bd. 15, p. 140), 

 placed living Cydippe in a solution of i in 4,000 of methylen blue in sea- 

 water, and upon sectioning the Cydippe he claims to have found a sub- 

 epitheUal network of nervous nature. This consists of large, ganglionic 

 cells scattered at fairly regular intervals. Each of these cells gives rise 

 to 3 or 4 protoplasmic processes which fuse with like processes from other 

 ganglia, thus appearing to form a nervous network without separate 

 neurons; a condition so extraordinary that confirmatory studies must 

 be made before we can accept it as proven. 



The experiments of Parker upon Mnemiopsis lend support to the 

 conclusion that nervous elements may extend outward from the apical 

 sense-organ along under the combs of ciUa, or at any rate the normal 

 rhythm of the ciliary combs is controlled by the nervous or muscular 

 elements. I now find that in ctenophores when the muscles contract 

 the cilia cease to beat, being inhibited by the stretching of the ciHated 

 epitheHum. A solution of 0.4 molecular MgClj, which inhibits mus- 

 cular movement and produces relaxation, causes an incessant and very 

 active movement of the cilia, but coordinated movements of the rows 

 of combs are usually destroyed, each comb beating independently of 

 its neighbors and at an exceedingly rapid rate, uncontrolled by the 

 nervous system. In M. mccradyi, however, coordination is retained. 



From the physiological side there is evidence, but no proof, to sup- 

 port the view that there is in ctenophores a nervous system compara- 

 ble to that seen in higher metazoa. The results of such physiological 

 researches are stated in this paper under Nmemiopsis and Bero'e. 

 Recently Bauer, 1910, Zeitschrift fiir Allgemeine Physiol., Jena, Bd. 10, 

 p. 231; concludes that the combs of ctenophores are under the control 

 of a nervous system. He states that the nervous system can produce an 

 acceleration or a retardation of the movements of the combs. Weak 

 mechanical stimuli such as touching the mouth-region cause a stopping 

 of the combs, while strong stimuli cause an acceleration. The sensory 

 pole is without significance for this reflex. A summation of weak 

 stimuH produces finally the effect of a single strong stimulus, and thus 

 ctenophores show the well-known " treppe " effect which has been 

 observed in higher forms. 



